In vitro dielectric properties of human tissues at radiofrequencies

In vitro permittivity measurements of excised human liver, spleen, kidney and cardiac muscle at frequencies from 10 kHz to 100 MHz are described. An end-of-the-line capacitive sensor and a computer-controlled network analyser HP 3577 were employed. The results were compared with human data reported by other investigators as well as with the animal (cat) data obtained earlier in this laboratory. It was found that the conductivity of most of the human tissues tested was significantly higher than that of the animal tissues for the test frequencies. The dielectric constants for human kidney and spleen are higher than the corresponding animal (cat) tissues at frequencies from 10 kHz to approximately 1 MHz and at around 100 MHz. However, the values for liver do not differ significantly between the two species in the same frequency range.     

Correction of electrode polarization contributions to the dielectric properties of normal and cancerous breast tissues at audio/radiofrequencies

Spurious contributions from electrode polarization (EP) are a major nuisance in dielectric measurements of biological tissues and hamper accurate determination of tissue properties in the audio/radiofrequencies. Various electrode geometries and/or treatments have been employed traditionally to reduce EP contributions, although none succeeded to completely remove EP from measurements on tissues for all practical frequency ranges. A method of correction for contributions of EP to the dielectric properties of tissues is proposed. The method is based on modeling the electrode impedance with suitable functions and on the observation that certain parameters are only dependent on electrodes properties and can thus be determined separately. The method is tested on various samples with known properties, and its usefulness is demonstrated with samples of normal and cancerous human female breast tissue. It is observed that the dielectric properties of the tissues over the frequency range 40 Hz-100 MHz are significantly different among different types of breast tissue. This observation is used further to demonstrate that, by scanning the tip of the measuring dielectric probe (with modest spatial resolution) across a sample of excised breast tissue, significant variations in the electrical properties are detected at a position where a tumor is located. This study shows that dielectric spectroscopy has the potential to offer a viable alternative to the current methods for detection of breast cancer in vivo.     

In vivo and in vitro dielectric properties of feline tissues at low radiofrequencies

The dielectric constant and conductivity of muscle, liver, spleen and kidney of cats in vivo and in situ immediately following the animal's death were measured at frequencies from 10 kHz to 100 MHz. A novel multi-ring capacitive sensor and a computer-controlled automatic network analyser (ANA) were employed. The results were compared with the data available from literature for the same species in the frequency range between 10 and 100 MHz. It was found that at frequencies from 10 to 100 kHz the in vitro dielectric constant for all tissues except spleen was smaller than the in vivo one. In contrast, in the range from 1 to 100 MHz the in vitro dielectric constant was larger than the in vivo one. At intermediate frequencies from 0.1 to 1 MHz both the dielectric constant in vivo and in vitro were the same within the experimental uncertainty. The dielectric constant of the spleen in vivo was quite similar to that in vitro. The in vivo conductivity of all tissues appeared to be higher than in vitro from 10 kHz to 10 MHz, while at frequencies above 10 MHz the two conductivities were within the experimental uncertainty.     

Dielectric properties of female human breast tissue measured in vitro at 3.2 GHz.

Complex permittivities of in vitro diseased and undiseased human female breast tissues have been measured at 3.2 GHz using a resonant cavity technique. Ranges of dielectric properties and water contents of these tissues are presented. Experimental data are compared with models predicted from mixture equations. Measured permittivity data lie within limits set by two-phase mixture theory, but some conductivity data are in excess of those expected for a mixture of saline and protein. At any particular microwave frequency in all tissue of a given type, the relationship between permittivity and conductivity may be parametrized using the Debye relaxation equations. For each breast tissue type a characteristic relaxation frequency was calculated and found to be lower than that of physiological saline at the same temperature. It is concluded that the dielectric relaxation of tissue water is not the only dispersive process occurring at this frequency: dielectric relaxation of bound water and the tail end of a beta-dispersion may also contribute to the dielectric properties. The similarity of the dielectric properties of benign and malignant breast tumours measured in this work suggest that in vivo dielectric imaging methods will not be capable of distinguishing them.     

Dielectric properties of mammalian brain tissue between 1 and 18 GHz

A newly developed frequency domain technique was used to measure the dielectric properties of white matter, grey matter and macerated rabbit brain at 20 and 37 degrees C. An analysis of the data showed that between 1 and 4 GHz there were substantial contributions from processes other than the gamma dispersion. However, above 7.5 GHz it appeared that mainly free water was relaxing although evidence of a small spread of relaxation times was found for the bulk water in the white matter. Mouse and rat brain were also measured but no significant differences were found between the species. The quantity of bound water was estimated but there was no evidence of a difference in the amount between either the tissues or the temperatures.     

MRI拉莫尔频率范围内人体脑胶质瘤组织的介电特性

目的:研究人体脑胶质瘤组织在MRI拉莫尔频率范围内（50~500 MHz）的介电特性,建立人体脑胶质瘤组织介电参数频率谱图,为磁共振断层成像技术提供理论依据和数据参考。方法:以神经外科手术中切下的脑胶质瘤组织为标本,在温度为37 °C的恒温水箱中,利用开端同轴线法,在50~500 MHz频率范围内使用AV 3656A网络分析仪测量脑胶质瘤组织标本的介电特性。以四阶Cole-Cole模型为基础,利用最小二乘曲线拟合方法,提取人体脑胶质瘤组织的介电特征参数。同时,将实验测得的脑胶质瘤组织介电特性与健康人体组织介电特性数据库中的正常脑组织进行比较。结果:在测频率范围内,人体脑胶质瘤组织实测数据与Cole-Cole模型吻合良好,且有人体脑胶质瘤组织的相对介电常数比正常脑组织高29.5%~36.6%,电导率比正常脑组织高56.1%~64.8%。结论:本文报道了37 °C下人体脑胶质瘤组织在MRI拉莫尔频率范围内（50~500 MHz）的介电特性数据及相应的Cole-Cole模型介电特征参数,可为人体脑胶质瘤组织介电特性研究和磁共振断层成像技术提供基础数据。     

Effect of temperature on the RF dielectric properties of human breast milk

The dielectric dispersion of human breast milk has been investigated by means of a resonance technique over the frequency range 0.1-100 MHz and at six temperatures from 10 to 60 degrees C. A computer analysis of the data was carried out on the basis of the Cole-Cole structural model and the fitted parameters have been presented. The dependence on temperature of both the viscosity of the human milk and its dielectric relaxation has been discussed. The heat of activation delta H of the milk, calculated in accordance with Eyring's theory of rate processes was found to be 19.5 +/- 0.6 kJ mol-1 for the dielectric relaxation process and 20.2 +/- 0.8 kJ mol-1 for viscous flow.     

Antibacterial properties of breast milk: Requirements for surface phagocytosis and chemiluminescence

The opsonic components of breast milk responsible for phagocytosis of surface-adherentStaphylococcus aureus by human polymorphonuclear leukocytes were investigated. There was significantly greater phagocytosis of bacteria pre-opsonized with 100 % breast milk than of unopsonized bacteria (p<0.001). Heat inactivation of breast milk had no effect on surface phagocytosis, indicating that phagocytosis is independent of complement. The predominant immunoglobulin in breast milk, secretory immunoglobulin A (IgA), did not promote phagocytosis. In contrast, IgG, which is present in very low amounts in breast milk (0.05 mg/ml), was as opsonic as 100 % breast milk, suggesting that this is the major opsonin. An oxidative burst as measured by chemiluminescence was observed during phagocytosis of bacteria pre-opsonized with 100 % breast milk. Heat inactivation of breast milk reduced the chemiluminescence response to the level of control. Neither secretory IgA nor IgG stimulated a polymorphonuclear leukocyte chemiluminescence response to surface-adherent bacteria. These experiments indicate that IgG is the principal component of breast milk responsible for surface phagocytosis but that complement is required for the generation of chemiluminescence and thus may be essential for intracellular killing of bacteria. Secretory IgA, despite its abundance in breast milk, has no effect on surface phagocytosis or neutrophil chemiluminescence.     

Passage of cows' milk protein in breast milk

An enzyme-linked immunosorbent assay has been used to search for lactoglobulin and bovine casein in breast milk. Initial results suggest this may be a simple and useful method for such studies. Detection and prevention of antigen passage could influence the prevalence of atopic disease.     

Dielectric properties of low-water-content tissues

The dielectric properties of two low-water-content tissues, bone marrow and adipose tissue, were measured from 1 kHz to 1 GHz. From 1 kHz to 13 MHz, the measurements were performed using a parallel-plate capacitor method. From 10 MHz to 1 GHz, a reflection coefficient technique using an open-ended coaxial transmission line was employed. The tissue water contents ranged from 1 to almost 70% by weight. The dielectric properties correlate well with the values predicted by mixture theory. Comparison with previous results from high-water-content tissues suggests that bone marrow and adipose tissues contain less motionally altered water per unit dry volume than do the previously studied tissues with lower lipid fractions. The high degree of structural heterogeneity of these tissues was reflected in the large scatter of the data, a source of uncertainty that should be considered in practical applications of the present data.     

Dielectric properties of biological tissue at low temperatures demonstrated on fatty tissue.

Dielectric behaviour of fatty tissue was investigated from T = 300 K to 4 K and f = 20 Hz to 1 MHz. Characteristic curves were obtained only at low frequencies. With decreasing temperature four important features were detected: the water-ice transition at T = 265 K, a relaxation process of the fat molecules (near 260 K) and one connected with the ice-part (210 K-170 K). The reason for the fourth relaxation at T = 140 K has not been fully understood yet: it may be caused by segmental rotation of the fatty acid molecules or the presence of multiple bonds. The epsilon"-maximum caused by the ice relaxation at T congruent to 200 K can be used to detect successful application of cryotherapy, i.e. the temperature fall below the minimum value of 233 K.     

Dielectric relaxation properties of linear polythioethers

Values of the dielectric loss tangent were obtained as a function of temperature for poly(pentamethylene sulfide) (P5MS) and poly(1,3-dithiocane) (PDTC). Both P5MS and PDTC exhibit a β absorption, located in the vicinity of their respective glass transition temperatures, ?105°C and ?73°C, which is believed to be associated with micro-Brownian motions in the amorphous phase of the crystalline polymers. The glass-rubber transitions of the polymers are discussed in terms of the flexibility of the chains, as expressed by their conformational partition functions and entropies.     

Monitoring of drugs in breast milk

With the increasing popularity of breast feeding, the secretion of drugs in breast milk would be of clinical interest. The merits of breast feeding and the composition of breast milk are outlined. The pharmacokinetics of drugs in breast milk may be described by a 3-compartment open model, with breast milk being the third compartment--a deep compartment with limited capacity. Recent clinical studies on secretion of atenolol, propranolol, propoxyphene, phenytoin, carbamazepine, and valproic acid in breast milk showed that the infant ingested dose was insignificant. Thus, nursing mothers on these drug therapies should be allowed to breast feed their infants. Owing to the lack of adequate clinical data and methodology for studying the secretion of antidepressants in breast milk, there is a need for a sensitive assay. Thus, a reversed-phase high performance liquid chromatography assay of imipramine and desipramine in breast milk was outlined, with sensitivity of 5 micrograms per liter. With the instrumentational capability of most clinical laboratories, it would be possible to perform drug levels measurement in breast milk. In collaboration with other clinicians, a useful data base could be accumulated for making rational decisions on breast feeding for mothers on drug therapy.     

Poly(allylbenzene). Dielectric properties

Poly(allylbenzene) or poly(3-phenyl-1-propene) belongs to the family of poly-α-olefin polymers of known mechanical properties. After synthesis and characterization, the dielectric behaviour of this polymer was determined over a wide temperature range (?32°C to 107°C) at frequencies from 20Hz to 10kHz. The results contribute to the study of the relaxation spectroscopy of poly-α-olefins.     

Human immunodeficiency virus in breast milk

As the acquired immunodeficiency syndrome (AIDS) epidemic spreads to the pediatric population, a recommendation is made for more research on mother-to-infant human immunodeficiency virus (HIV) transmission, in light of current policies, and the scientific community is challenged to re-evaluate its attitude to the pathogenesis of HIV transmission by breast milk.